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Flight Performance - Level 3

Human Factors-Section 3

A. VISION

Good vision is of primary importance in flying, in judgment of distance, depth
perception, reading of maps and instruments and should, therefore, be scrupulously
protected.

Pilots; are exposed to higher light levels than is the average person. Very high light
levels prevail at altitude because the atmosphere is less; dense. In addition, light is
reflected back at the pilot by cloud tops. This light contains more of the damaging blue
and ultra-violet wavelengths than are encountered on the surface of the earth. Prolonged
exposure can cause damage to the eye and especially to the lens. Sunglasses should,
therefore, be worn to, provide protection against these dangers and to prevent eyestrain.

Instrument panels should be dull grey or black, to harmonize with the black
instruments, so that the eye does not have to adjust its lens opening constantly as the
line of vision moves from the dark instruments to a light colored panel.

When flying into, the sun, the eyes are so dazzled by the brightness that they cannot
adjust quickly to the shaded instrument panel. This situation causes eyestrain and is
fatiguing to the pilot. Sunglasses help to minimize the problem.

Atmospheric obscuring phenomena such as haze, smoke and fog have an effect on the
distance the normal eye can see. The ability of the eye to maintain a distance focus is
weakened. Distant objects are not outlined sharply against the horizon and after a short
lapse of time the eye, having no distance point to fix on, has difficulty maintaining a
focus at a distance of more than a mile or two, (a condition known as empty field myopia).
As a result, scanning for other aircraft becomes difficult and requires special effort on
the part of the pilot. With the pilot's focal range reduced, the span of time in which to
perceive the danger and take evasive action is considerably shortened. Pilots must learn
to recognize the limitations of the human eye under varying weather conditions and realize
that the see and avoid maxim has limitations under some atmospheric conditions.

Depth Perception. Clues for accurate depth perception are often absent in the
air. Clouds are of varying size and there is no way to estimate their distance. Landings
on glassy water or on wet runways are a problem as is the condition known as white out
that occurs in blowing snow and other winter situations.

Night Vision. At night, the pilot's vision is greatly impaired. The cones
that are concentrated in the center of the lens need a lot of light to function properly.
As a result, there is a blind spot in the center of the eye at night. This blind spot is
sufficiently large to block out the view of another airplane some distance away if the
pilot is looking directly at it.

At night, it is necessary to develop the technique of using peripheral vision. One sees
at night by means of the rods that are concentrated on the edges of the lens and are
responsible to peripheral vision. It takes the rods about 30 minutes to adjust full to
darkness. Even a small amount of white light will destroy the dark adaptation.

Pilots should wear sunglasses during the day and avoid looking at bright lights when
they propose to undertake a night flight. Wearing red goggles for 30 minutes prior to a
night flight helps their eyes adapt to darkness.

Night vision is also sensitive to hypoxia. Supplementary oxygen should be used above
5000 feet to avoid depriving the eye of oxygen.

Dirt and reflection on the windshield cause confusion at night A very clean windshield
is important.

Night Lighting of Instruments. Lighting of instruments is a problem in that the
instruments must be well enough lit to be readable without the light destroying the
pilot's dark adaptation.

Ultraviolet flood fighting of fluorescent instrument marking is probably the least
satisfactory. The instruments are marked with fluorescent paint that shows up under
fluorescent lighting as a bluish green color. The disadvantages are that the instruments
can't be kept in focus, dark adaptation may be lost, eyes are irritated, vision becomes
foggy.

Red lights. Lighting of instruments by indirect individual red lights; is
unsatisfactory because uniform light distribution over al, parts of the instrument cannot
be achieved. There is no illumination of knobs and switches. Red flood lighting of the
whole instrument panel is more satisfactory. However, the ability to distinguish colors
one from another is lost. Coloration of maps is indecipherable and information printed in
red becomes unreadable.

White lights. Low density white, light is considered the best cockpit lighting
system. The instruments can be clearly read and colors recognized. Because the low density
white light can be regulated, dark adaptation is not destroyed although it is somewhat
impaired.

Thunderstorms. It is not advisable to fly an airplane through or near
thunderstorms. The blinding flashes destroy night adaptation. Turn the cockpit lights full
bright if you are in the vicinity of lightning activity in order to prevent lightning
blindness.

Anti Collision Lights. When flying in the clouds, strobe lights and rotating
beacons should be turned off as the reflection off the cloud of the blinking light is
irritating to the eye.

B. NOISE, VIBRATION AND TEMPERATURE

NOISE

Noise is both inconvenient and annoying. It produces headaches, visual and auditory
fatigue, airsickness and general discomfort with an accompanying loss of efficiency. Even
at levels which are not uncomfortable, noise has a fatiguing effect, especially when the
pilot is exposed for a long period as on a lengthy cross country flight. To arrive at
destination suffering from noise induced fatigue and have to, make a landing under minimum
conditions is clearly an undesirable situation.

Noise levels in the range of 130 decibels or above are very dangerous and should not be
experienced without ear protection . (The unit of sound intensity or loudness is called
the decibel or db.) Yet, little has been done to reduce and control noise in aircraft
cockpits. Tests; have measured the sound level in modern aircraft at 90 to 100 decibels.
Noise levels in jets can approach 140 decibels.

With noise levels of this magnitude, hearing damage is a distinct problem unless some
sort of hearing protection is used. Many pilots report temporary loss of hearing
sensitivity after flights. Still others have reported an inability to understand radio
transmissions from the ground, especially during take-off and climb when the engine is
operating at full power. In fact, there is documented evidence to show that continued
exposure to high levels of aircraft noise will result over the years in loss of hearing
ability.

The detrimental effect of noise is not a sudden thing but builds up progressively over
years of exposure. Pilots of helicopters and aerial application aircraft are particularly
susceptible because of the relatively high levels of noise experienced in these cockpits
and the long duration of exposure. But even pilots, who put in only three or four hours a
week in their airplanes, have been found to have slightly impaired hearing after several
years.

Everyone experiences some hearing deterioration as the process of growing old. Add this
to a level of deafness caused by exposure to noise and it becomes obvious that a pilot
reaching middle age could have a serious hearing deficiency.

Protective devices against noise are therefore important, first of ail, in helping to
reduce fatigue during individual flights and, secondly, in helping to minimize the
possibility of hearing loss or deterioration in later years.

The best protection is a pair of properly fitting earplugs. They lower noise levels by
as much as 20 to 30 decibels. The use of ear covering devices, such as earphones. can also
help if they are fight fitting. If they fit poorly, they can be worse than nothing, in
that they give the wearer a false sense of security. The use of earplugs as well as
earphones is recommended.

The wearing of earplugs does not impair ability to hear. In fact, speech
intelligibility is improved because the earplugs filter out the very noises that interfere
with voice transmissions.

The regular wearing of earplugs, especially by pilots but also by passengers. is
therefore a good precautionary measure to ensure continued good hearing throughout a
pilot's lifetime.

VIBRATION

The power plant of the airplane is the principal source of vibration. At subsonic
speeds, this vibration is responsible for fatigue and irritability and can even cause
chest and abdominal pains, backache, headaches, eyestrain and muscular tension. If the
vibration happens to occur in the frequency of about 40 cycles per second, the eyes will
blur. It is even possible to become hypnotized as a result of rhythmic and monotonous
vibrations.

TEMPERATURE

At temperatures over 30° C, discomfort, irritability and loss of efficiency are
pronounced. High temperatures also reduce the pilot's tolerance to mental and physical
stresses, such as acceleration and hypoxia.

At cold temperatures, the immediate danger is frostbite. Continued exposure will result
in reduced efficiency to the point where safe operation of the airplane is impossible.

Hypothermia. The most serious result of extended exposure to extremely cold
temperatures is a condition known as hypothermia. Hypothermia is a lowering of the
temperature of the body's inner core. It occurs when the amount of heat produced by the
body is less than the amount being lost to the body's surroundings. As it progresses,
vital organs and bodily systems begin to lose their ability to function. It is a condition
that can develop quickly and may be fatal.

In the early stages, the skin becomes pale and waxy, fatigue and signs of weakness
begin. As the body temperature drops farther, uncontrollable intense shivering and
clumsiness occur. Mental confusion and apathy, drowsiness, slurred speech, slow and
shallow breathing are the next stage. Unconsciousness and death follow rapidly.

Hypothermia certainly can attack a pilot in the cockpit of his airplane if there is no
cabin heating system and if he is not adequately dressed to protect against very cold
ambient temperatures. Usually, however, hypothermia is considered to be a danger to the
pilot who has been forced down and is exposed to the elements. Cold, wetness, wind and
inadequate preparation are the conditions which cause it. Wet clothing, caused by weather,
immersion in water or condensed perspiration, acts like a wick and extracts body heat at a
rate many times faster than would be the case with dry clothing. Immersion in cold water
greatly accelerates the progress into hypothermia.

The best protection against this condition is adequate clothing, shelter, emergency
rations and, above ail, knowledge of the danger. Every wintertime flier should have a
survival kit that includes a lightweight tent, plastic sheet, survival blanket, etc., that
can be used to construct a shelter. Always wear (or take along as extras) proper clothing
for the worst conditions you might encounter. Several layers of clothing are more
effective than one bulky layer. Protect high heat loss areas, such as the head, neck,
underarms, sides of the chest. Carry effective rain gear and put it on before you get wet.
High energy foods that produce heat and energy should be included in the survival kit. Hot
fluids help to keep body heat up. Guard against becoming tired and exhausted, A tired
person, exposed to a cold ,wet and windy environment, is a prime candidate for
hypothermia.

C. SENSORY ILLUSIONS

Under normal conditions, the eyes, inner ears and skeletal muscles provide the brain
with information about the position of the body in relation to the ground. In flying,
however, conditions are sometimes encountered which fool the senses.

The eyes are the prime orienting organs but are dependent on reference points in
providing reliable spatial information. Objects seen from the air often look quite
different than they do when seen from the ground. If the horizon is not visible, a pilot
might choose some other line as reference, such as a sloping cloud bank. Fog and haze
greatly affect judgment of distance. Lights on the ground at night are commonly confused
for airplanes. Even stars can be confused with ground lights.

The tension of various muscles in the body assists in a small way in determining
position. The body is accustomed to the pull of one g force acting in only one direction.
In an airplane. if a second force is introduced as in acceleration, deceleration and
turns, and if there is no outside visual reference, illusions may result. For example, in
a bank, both centrifugal force directed outward and the normal downward pull of gravity
combine to give an illusion of level flight. Acceleration gives an illusion of climbing
and deceleration of diving.

The three semicircular canals of the inner ear are primarily associated with
equilibrium. They are filled with fluid and operate on the principle of the inertia of
fluids. Each canal has tiny hair like sensors that relate to the brain the motion of the
fluid. Rotation of the body tends to move the fluid, causing the displacement of the
sensors which then transmit to the brain the message of the direction of their
displacement. However, if the turn is a prolonged and constant one the motion of the fluid
catches up with the canal walls, the sensors are no longer bent and the brain receives the
incorrect message that the turning has stopped. If the turn does then indeed stop, the
movement of the fluid and the displacement of the sensors will indicate a turn in the
opposite direction. Under instrument conditions or at night when visual references are at
a minimum, incorrect information given by the inner ear can be dangerous.

The following factors contribute to visual illusions: optical characteristics of
windshields; rain on the windshield; effects of fog, haze, dust, etc. on depth perception;
the angle of the glide slope makes a runway appear nearer or farther as does a very wide
or very narrow runway; variations in runway lighting systems: runway slope and terrain
slope; an approach over water to the runway; the apparent motion of a fixed light at night
(auto-kinetic phenomenon). The visual cues by which a pilot makes judgment, about the
landing approach are largely removed if the approach is over water, over snow or other
such featureless terrain or carried out at night. A particularly hazardous situation is
created if circumstances prevent him from appreciating ground proximity before touchdown.

The following factors contribute to sensory illusions: change in acceleration or
deceleration; cloud layers; low level flight over water, frequent transfer from instrument
to visual flight conditions (choose either VFR or IFR and stick with the choice);
unperceived changes in flight altitude.

There is just one way to beat false interpretation of motion. Put your faith in your
instruments and not in your senses.

Refer to the altitude Instruments constantly when flying at night or In reduced
visibility conditions.

Spatial disorientation means loss of bearings or confusion concerning one's sense
of position or movement in relation to the surface of the earth. Disorientation rarely
occurs without reduced visual references in such situations as fog, cloud, snow, rain,
darkness, etc.

A type of spatial disorientation is caused in some individuals by flickering shadows.
When, for example, letting down for a landing into the setting sun with a single engine
airplane, the idling propeller can induce reactions that range from nausea to confusion
and, in rare cases, complete unconsciousness. Other causes of this sensation are
helicopter rotor blade shadows, the flashing illumination caused by anti-collision lights
when flying in clouds, and runway approach strobe lights when viewed through the propeller
at night.

The term vertigo is sometimes used in relation to spatial disorientation.
Vertigo is a sensation of rotation or spinning, an hallucination of movement of either the
individual himself or of the external world.

Coriolis effect is probably the most dangerous type of disorientation. The three
semicircular canals of the inner ear are interconnected. If movement is occasioned in two
of them, a sympathetic but more violent movement is induced in the third. This is known as
tumbling and causes extreme confusion, nausea, and even rolling of the eyeballs that
prevents; the pilot from reading correctly the airplane instruments. This situation can
occur if, when the airplane is in a turn, the pilot suddenly turns his head in another
direction. The rule should always be to avoid head movements, especially quick ones, when
flying under instrument conditions.

Otolith-False Climb Illusion. The otolith is a small organ which forms part
of the inner ear, and vestibular apparatus. Its function is to sense and signal to
the other organs the position of the head relative to the vertical. This signal has a
profound influence on the balance and orientation of the body.

The otolith, simply described, is an erect hair with a small weight or mass at its tip.
The base of the hair is embedded in a sensory cell which conveys to the brain information
about the angle of the hair.

When the head is tilted backward, the small mass bends the hair and the message relayed
to the brain indicates a backward tilt. If the head is held vertical but is subjected to
acceleration, the hair bends owing to the inertia of the mass at the tip of the hair. Both
tilt and acceleration, therefore, produce the same response by the, otolith. If there are
no visual cues to compliment the information from the otolith, the brain is unable to
differentiate between till and acceleration. If tilt and acceleration are experienced
simultaneously the interpretation is that of a much steeper tilt. This is known as the false
climb Illusion.

In such a situation, a pilot is tempted to lower the nose of the airplane. This
increases the forward acceleration component and increases the illusion of climbing
steeply. Owing to lag in the altimeter and vertical speed indicator, the loss of height
may go unnoticed.

There are three situations in which the false climb illusion may occur: (1) take-off at
night or in IFR conditions, (2) an overshoot in reduced visibility or in IFR conditions,
and (3) a climb from VFR into IFR conditions. During the latter situation, the illusion
can be com pounded by turbulence, in a turn, or by reliance on an artificial horizon that
is not quite erect.

All pilots irrespective of experience or skill are susceptible to the illusion. Pilots
must learn to anticipate the illusion and ignore it, to establish a positive climb
attitude and to rely on the aircraft instruments for confirmation of attitude.